The present invention relates to a method for separating organic phosphorus-ruthenium complex as a catalyst, a method for reusing the same, a process for preparing .gamma.-butyrolactone, and a method for recovering an organic phosphorus compound as ligand. More particularly, the present invention relates to a method for separating a ruthenium complex and/or an organic phosphorous compound as a catalyst or a ligand thereof from products of hydrogenation reaction of a dicarboxylic acid or a derivative thereof using a ruthenium complex having a tertiary organic phosphorous compound as ligand, a method for reusing the separated ruthenium complex, etc., for the hydrogenation reaction, a process for preparing .gamma.-butyrolactone (GBL) from the hydrogenation reaction of succinic anhydride by reusing the separated ruthenium complex, and a method for recovering a tertiary organic phosphorous compound as a catalyst ligand from the hydrogenation reaction product.
Organic phosphorus-ruthenium complex having a tertiary organic phosphorus compound as ligand is used as catalyst for the homogenous-system catalytic hydrogenation reaction of various kinds of carbonyl compounds. Since this ruthenium complex catalyst is relatively stable in chemical properties, in the hydrogenation reaction system using such catalyst, the reaction product and the catalyst solution can be separated by distillation and the separated catalyst solution can be recycled to the reaction vessel for reuse. Also, the reaction product can be effused out of the reaction vessel by gas stripping and the reaction can be carried out continuously with the catalyst solution remaining in the reaction vessel. However, in these reactions, there are inevitably formed various high-boiling by-products, and in case where the reaction is carried out continuously, since the high-boiling substances are accumulated in the catalyst solution, it is necessary to discharge a part of the catalyst solution from the reaction system continuously or intermittently.
Since ruthenium is contained in the discharged solution, a proper treatment is required in disposal thereof. However, as from the solution containing ruthenium, when burned, RuO.sub.4 which is poisonous and has strong corrosiveness is produced, the burning treatment of the solution for its disposal is undesirable. Also, economical problem is involved in an industrial waste disposal of the solution containing ruthenium, since cost equivalent to the mass of the solution to be treated, is charged when the amount of the solution to be treated is large. Therefore, if ruthenium in the discharged solution can be concentrated, its economical effect will be very great. Further, if ruthenium complex can be recovered efficiently from the discharged solution and reused for the reaction, it will be possible not only to greatly reduce the expenses for disposal of the solution containing ruthenium but also to remarkably lessen the cost for catalyst. This is, also, favorable from the viewpoint of prevention of environmental pollution, since the absolute amount of ruthenium released into the atmosphere is reduced. For attaining this, however, it is necessary to separate and recover the complex catalyst retaining its active state from the reaction solution.
Hitherto, as methods for separating and recovering VIII Group metals such as rhodium, there have been known an extraction method using a strong acid (Japanese Patent Publication (KOKOKU) No. 46-43219) and a decomposition method using a peroxide (U.S. Pat. No. 3,547,964 and Japanese Patent Application Laid-Open (KOKAI) No. 51-63388). However, any of these methods involved the problem of corrosion of the apparatus, since an acid is used in these methods.
As a result of the present inventors' earnest studies for the economical and efficient recovery of a ruthenium complex having a tertiary organics phosphorus compound as ligand from a hydrogenation reaction solution of an organic carbonyl compound and for reuse of the recovered ruthenium complex for the hydrogenation reaction, it has been found that by separating an objective product and as occasion demands, a reaction solvent from the hydrogenation reaction solution, and contacting the resultantly obtained catalyst solution with a polar solvent, it is possible to recover an organic phase rich with ruthenium complex and/or organic phosphorus compound, and to reuse the recovered ruthenium complex as a catalyst component for the hydrogenation reaction. The present invention has been attained on the basis of this finding.